OBJECTIVE: To define the antigenic changes on the cell surface of developing myoblasts and to identify which of these components are germane to the differentiation and fusion of these cells. Comparisons of the membranes of the normal myogenic cells with developmentally defective transformed and tumorigenic mutants will be made. APPROACH: Monoclonal antibodies directed against cell surface determinants will be prepared and used to isolate and quanitfy antigenic membrane components present on the differentiating myoblast and on their transformed counterparts.